1. Field of the Invention
This invention generally relates to enzyme catalyzed processes for producing chiral .beta.-amino acids. In particular, this invention relates to processes for producing chiral .beta.-amino acids employing Penicillin G acylase.
2. Related Background Art
The current evolving regulatory climate in the development of chiral drugs has created the necessity of preparing highly optically active compounds in pharmaceutical, agricultural and chemical industries. This development has presented many opportunities to synthetic chemists who are interested in the development of new chirotechnology. In recent years there have been explosive advances in the development of new synthetic methods, including asymmetric syntheses, stereoselective crystallization, chiral chromatography, racemate resolution and catalytic kinetic resolution, to prepare optically pure compounds. Despite these new developments, there are still relatively few efficient scalable chirotechnologies capable of producing multikilogram to ton quantities of optically active compounds economically.
Enzyme-catalyzed syntheses have been used in the commercial production of chiral pharmaceuticals. We have developed a new process for the preparation of chiral .beta.-amino acids or their corresponding esters using enzyme-catalyzed acylations or enzyme-catalyzed deacylations.
Penicillin G acylase is a serine hydrolase with a high specificity for the acyl side chain (phenylacetyl) but a low selectivity for the amino side chain (R. Didziapetris et al., (1991) FEBS Letters 287 (1,2), 31). The enzyme is comprised of two subunits, .alpha. and .beta., each of which may have activity (70% for the .alpha., 30% for the .beta. chain) (V. E. Kabakov et al., (1995) Biochemistry (Moscow) 60 (5), 593; I. Prieto et al. (1990), Appl. Microbiol. Biotechnol. 33, 553).
Penicillin G acylase has traditionally been used to hydrolyze penicillin G (See, for example, J. G. Shewale and H. Sivaraman, (1989) Process Biochemistry, August, 1989, 148; F. Ishimura and K. Suga, (1992) Biotechnol. Bioeng. 39 (2), 171; J. Bryjak et al., (1996) Enzyme And Microbial Technology 19, 196).
The use of acylases in the preparation of alpha amino acids is known (Greenstein, J. P.; Chemistry of the Amino Acids; Wiley: New York, 1961; Greenstein, J. P.; Method. Enzymol. 1957, 3, 554; Chibata, I; Method. Enzymol. 1976, 44, 554; Chenault, H. K.; J. Am. Chem. Soc. 1989, 111, 6354.). The use of Penicillin acylases in the resolution of gamma amino acids using enzymatic deacylation was reported in WO 94/02628. Enzymatic acylation was not reported in this work.
The use of Penicillin acylases in the resolution of beta amino acids using enzymatic deacylation has been reported (Soloshonok; SYNLETT, 1993, 339; Soloshonok; Tetrahedron Asymmetry, 1994, 5, 1119; Soloshonok; Tetrahedron Asymmetry, 1994, 5, 1225) However, enzymatic acylation was not reported in this work and the beta amino acids used for the deacylation do not contain any alkynyl or alkenyl functions, which are key beta amino acids leading to active anti-platelet drug candidates.
The use of Penicillin acylases in the acylation of beta lactam intermediates was reported in 1991 (Zmijewski, M. J.; Tetrahedron Letters, 1991, 32, 1621). No work on beta amino acids was reported in this work.
This invention is useful for preparing compounds that contain chiral beta amino acids or their derivatives. The chiral .beta.-amino acids and their derivatives are useful for making pharmaceuticals, such as antiplatelet agents (Zablocki et al, J. Med. Chem., 1993, 36, 1811; Bovy et al, Bioorg. Med. Chem, 1994, 2, 881-895; Zablocki et al, J. Med. Chem., 1995, 38, 2378; U.S. Pat. No. 5,424,334; U.S. Pat. No. 5,481,021), immunological response modifiers (Suda et al, J. Antibiot., 1976, 29, 100), anti-hypertensive agents (Chaturvedi et al, J. Med. Chem., 1970, 13, 177; Lizuk at al, J. Chem. Soc., Chem. Commun., 1989, 1978; Okino et al., Tetrahedron Lett., 1993, 34, 501); and anticancer agents (Denis et al., J. Org. Chem., 1990, 55, 1957).